1. Field of the Invention
This invention relates to the field of simulation and more particularly to the acoustical presentation of simulated active sonar return signals.
2. Description of the Related Art
Active sonar provides a means for detecting and tracking submerged or surfaced contacts. Contacts are defined as reflective surfaces of interest (either physical surfaces or conditions having the reflective properties of physical surfaces). which reflect Sound propagated by a sonar emitter. The active sonar emits a pulse of acoustic energy into the water. In active detection, pulses of acoustic energy generated by the sonar are propagated through the water to the contact. Reflected from the contact, these pulses of acoustic energy travel back to a receiver. Range information is obtained by electronic circuitry that measures the time interval between transmitted and received pulses.
Typically, full physical models are used for high fidelity simulation of underwater passive emanations and active sonar signal reflections and the associated reverberation. Reverberation is a characteristic of underwater sound transmission caused by the environmental and physical characteristics and environment of the sea, the sea bottom, sea volume characteristics, and the sea surface that bound transmission. Reverberation introduces a noisier background environment that may mask the signals of interest reflected from the contacts.
The full physical reverberation modeling approaches used in the prior art are computationally intensive. Modeling reverberation typically requires one or more computers, each having the capacity for substantial central processor unit (CPU) cycles. The large processing requirement results because transmission loss calculations are required to be performed for all the directions that each acoustic transmitter emits. Each transmission loss calculation is modeled along a non-linear (ray path) radial from the emitter, and the transmission loss calculation requires many of these radials for the horizontal emission, and further requires the same number of radials to angle up and down at numerous intervals to get the full effect of the reverberation. This results in many returns that travel many different paths that may include surface and bottom reflections, and requires having to perform numerous transmission loss calculations to simulate the signal paths with high fidelity. High fidelity is a very important attribute to train sonar operators because the operators quickly learn to recognize repetitious environments that are not tied to changing simulated conditions.
When simulating a real environment with the full physical modeling approach, transmission loss calculations for all tactical areas become extensive. The extensive computational requirements render the CPU's unable to process results in real-time, unless enormous CPU resources are made available. In the context of real-time, the intent is that the computational resources must be able to simulate, in the virtual environment, contacts and tactical sensor and processing components quickly enough to provide realistic cause and effect situations to the trainee.
These computations are so extensive for obtaining real-time high fidelity results that obtaining real-time high fidelity results becomes cost prohibitive and, simulation fidelity is compromised because of limited hardware capabilities or availability. Therefore, there is a need to eliminate high CPU processing requirements for underwater acoustic active simulation, thereby allowing cost effective hardware solutions to perform real-time underwater active acoustic simulation.